Abstract:
Increased mechanization in the underground coal mining industry has decreased selectivity and increased the amount of refuse created. Coal preparation separates non-combustible material from coal. Thus, a coal preparation plant separates the material it receives into a product stream and a reject stream, which may be further divided into coarse and fine refuse streams. Depending on the source, 20 to 50 % of the run-of-mine material ends up in reject streams. One of the reject streams is a slurry stream. This is a blend of water, coal fines, silt, sand, and clay particles, which is commonly disposed of in an impoundment. There have been several incidents of impoundment breakthrough. Of these, Buffalo Creek in West Virginia in1972 and recently, Martin County Coal in Kentucky, have drawn the attention of federal and state governments and local people due to heavy losses of life and property.
In this project an advanced thickening technique known as “Paste Thickening Technology” marketed by the Dorr-Oliver EIMCO was evaluated at a coal preparation plant in West Virginia for the dewatering of fine coal tailings. The Deep Cone Thickener™ is specially designed to concentrate tailings into a high percent solid, so it can discharge as a paste. The thickened paste material could be stacked at a low angle of repose rather than stored in a pond. Thus, with utilization of this technique it is anticipated that the fine refuse slurry ponds could be completely eliminated.
The results obtained at the Coal Clean Corporation coal preparation plant showed that the Deep Cone Thickener™ was able to dewater the conventional thickener underflow material and produce a paste containing about 52.5 wt. % solids. The dewatered solids had the same moisture content as obtained by a belt filter machine. The Deep Cone Thickener™ was also able to dewater the centrifuge drain slurry, which consisted of clean coal product to about 70 wt. % solids.